Ground state entanglement in quantum spin chains

A microscopic calculation of ground state entanglement for the XY and Heisenberg models shows the emergence of universal scaling behavior at quantum phase transitions. Entanglement is thus controlled by conformal symmetry. Away from the critical point, entanglement gets saturated by a mass scale. Results borrowed from conformal field theory imply irreversibility of entanglement loss along renormalization group trajectories. Entanglement does not saturate in higher dimensions which appears to limit the success of the density matrix renormalization group technique. A possible connection between majorization and renormalization group irreversibility emerges from our numerical analysis.Comment: 26 pages, 16 figures, added references, minor changes. Final versio

Methane cracking over cobalt molybdenum carbides

The catalytic behaviour of Co3Mo3C, Co6Mo6C, Co3Mo3N and Co6Mo6N for methane cracking has been studied to determine the relationship between the methane cracking activity and the chemical composition. The characterisation of post-reaction samples showed a complex phase composition with the presence of Co3Mo3C, α-Co and β-Mo2C as catalytic phases and the deposition of different forms of carbon during reaction

Multicointegration, polynomial cointegration and I(2) cointegration with structural breaks. An application to the sustainability of the US external deficit.

In this paper we model the multicointegration relation, allowing for one structural break. Since multicointegration is a particular case of polynomial or I(2) cointegration, our proposal can also be applied in these cases. The paper proposes the use of a residualbased Dickey-Fuller class of statistic that accounts for one known or unknown structural break. Finite sample performance of the proposed statistic is investigated by using Monte Carlo simulations, which reveals that the statistic shows good properties in terms of empirical size and power. We complete the study with an empirical application of the sustainability of the US external deficit. Contrary to existing evidence, the consideration of one structural break leads to conclude in favour of the sustainability of the US external deficit.I(2) processes, multicointegration, polynomial cointegration, structural break, sustainability of external deficit.

Fine-grained entanglement loss along renormalization group flows

We explore entanglement loss along renormalization group trajectories as a basic quantum information property underlying their irreversibility. This analysis is carried out for the quantum Ising chain as a transverse magnetic field is changed. We consider the ground-state entanglement between a large block of spins and the rest of the chain. Entanglement loss is seen to follow from a rigid reordering, satisfying the majorization relation, of the eigenvalues of the reduced density matrix for the spin block. More generally, our results indicate that it may be possible to prove the irreversibility along RG trajectories from the properties of the vacuum only, without need to study the whole hamiltonian.Comment: 5 pages, 3 figures; minor change

El Refractòmetre d'Abbe, una eina important en la recerca i en la indústria : estudi d'un exemplar de principis del segle XX

Along the XIXth century there were great advances in the astronomy and the microscopy fields thanks to the improvements in the image quality obtained through the objectives of the telescopes and microscopes. This improvement was accomplished by the suitable combination of lenses with different refraction index reaching the correction of optical aberrations. In all this process it was essential to measure with precision the refraction index. Ernst Abbe in 1872 design his first model of refractometer based on the measure of the limit angle. The great advantage of his instrument was the simplicity of the design, the compactness, the good precision and the reduced size which was able to be a portable device. In this work a description, a study and analysis, including measurements, of an Abbe refractometer from the beginning of the XXth century are made

El nuevo campesinado emergente

Contiene la nota "Personas que luchan toda la vida, esas son las imprescindibles", de Jerónimo Aguado Martínez (Plataforma Rural).¿Quiénes serán las y los agricultores del día de mañana? ¿Qué prácticas utilizarán en sus fincas agrarias y qué actitudes mostrarán respecto al futuro de la agricultura y del mundo rural? Respondiendo a estas preguntas el artículo analiza y distingue dos grupos: las personas que relevan la actividad agraria familiar (campesinado tradicional) y las que entran por primera vez al sector agrario. ¿Qué conclusiones políticas podemos sacar de las diferencias entre estos dos colectivos